In the field of fire fighting there is a need for a pump assembly for a fire truck which is capable of delivering water at a first pressure to a first high flow rate fire fighting application, such as a 21/2 inch discharge fire hose, and to deliver water at a second pressure (substantially higher than said first pressure) to a second low flow high pressure fire fighting application, such as a booster pump reel.
In accordance with the invention there is provided a pump assembly of the indicated type that is inexpensive to construct, easy to operate and reliable. To this end, the pump assembly in accordance with the invention is provided with a main pump and a booster pump connected in series with the discharge of the main pump being delivered to a first high flow rate fire fighting application and to the inlet of the booster pump and the discharge of the booster pump being delivered to a second low flow high pressure fire fighting application. The impellers for both the main pump and the booster pump are mounted on a common rotating shaft so as to be driven thereby. In accordance with another feature of the invention a means are provided to reduce the pressure on the booster pump seal. In accordance with still another feature of the invention a by-pass conduit is arranged to conduct flow from the discharge of the booster pump back to the inlet of the main pump so that whenever the main pump is operated there will be flow through the booster pump to prevent overheating thereof.
The pump assembly of the invention involves simplicity and speed of operation. Both the booster pump and the main pump always operate together permitting the firemen to operate either the first or second fire fighting application or both of them together. Typically, the booster pump is connected to a booster pump line which is wrapped on a "live" reel and connected to a fog nozzle, and is usually placed into service as soon as possible when the fire truck arrives at the site of a fire and is supplied from a tank carried on the fire truck. It takes a high pressure to overcome friction of the booster reel's small diameter hose which uses a relatively small flow of water and can only operate for limited periods of time to dispense the tank water efficiently onto the fire. Maximum cooling effect or water vaporization can be achieved by the small volume booster fire stream if the stream is broken up into very fine particles through a fog nozzle. Also, since the reel's hose is much smaller and lighter than the 21/2 inch discharge hoses, it can be handled more easily and placed into service much more quickly. By reason of the construction of the pump assembly in accordance with the invention, the firemen can place in operation the main pump that supplies the 21/2 inch discharge hoses easily and without delay. This is achieved by simply opening the discharge valve to which the 21/2 inch discharge fire hose has been connected and without making any changes in the operation of the pump assembly or opening and closing a number of valves. Thus, the first and second fire fighting applications are performed concurrently and speedily. There is no need to slow down the drive to permit disengagement of the booster pump and engagement of the main pump as is the case with most types of fire fighting equipment in use today in which the booster pump and the main pump are driven by independent means. Thus, the prior art equipment involves a substantial time delay as compared with the pump assembly in accordance with the invention.
Another type of prior art pump assembly that has been used is designed to achieve the high pressure necessary to operate a booster reel by providing two impellers and means for operating the impellers in either series or parallel, the higher pressure operation being achieved by arranging the impellers in series. The discharge passage of this type of pump has available either high pressure low volume water in series or low pressure high volume water in parallel, but not both. Thus, such a pump cannot operate at two pressure levels unless an intermediate discharge from the first stage is provided, but this requires separate and expensive piping.
In accordance with another prior art pump assembly a third impeller is clutched onto the impeller shaft of a two stage pump and is connected to a low flow and high pressure application. However, this arrangement is unsatisfactory because it involves a high pressure seal at the third stage inlet, which high pressure seal is subject to excessive wear and premature failure. Additionally, the clutch is a source of mechanical problems, added expense and the pump has to be slowed down to engage and disengage the clutch.
Another feature of the pump assembly of the invention is that it is hydraulically engineered to provide the optimum hydraulic design for the impellers of both the main pump and the booster pump. This is not possible with the prior art pumps discussed above. In the typical series-parallel pump, the impellers are designed for much higher flow rates than would be handled by a booster line. For example, a series-parallel pump designed to operate at a flow rate of 1000 G.P.M. in the series arrangement, is designed so that each impeller handles 500 G.P.M. However, an impeller designed to handle 500 G.P.M. is not at all efficient when handling 30-50 G.P.M., which is the flow rate for a typical booster line application. In the pump assembly of the invention there is used a two stage booster pump having a small impeller diameter specifically designed for booster line applications. Such an impeller has a substantially lower power requirement as compared with the large diameter impellers of the prior art. Also, by reason of the small impeller diameter of the booster pump, there is very little drag (friction loss) on the main pump when the booster pump is not in use.
An additional feature of the pump assembly in accordance with this invention is that it can be retrofitted to existing fire trucks easily and can utilize previously available pump designs for both the booster pump and the main pump with minor modifications.